Refrigerating apparatus



Patented Oct. 18, 1932 UNITED STATES PATENT OFFICE WARREN H. F. SCHMIEDING, OF DAYTON,'OHIO, ASSIGNOR TO FR.IGIDAIRE CORPORA- TION, OF DAYTON, OHIO, A CORPORATION OF OHIO REFRIGERATING APPARATUS Application filed April 30,

The present invention relates to refrigerating apparatus and more articularly to refrigerating apparatus of the compression type wherein a lubricant is circulated in a closed circuit with the refrigerant.

Heretofore in refrigerating systems of the compression type trouble has been experienced because oil employed to lubricate operating parts of the system accumulated on top of the liquid refrigerant within the evaporator. This accumulation of oil within the evaporator becomes very viscous as the temperature of the evaporator is reduced, and forms a thick layer or blanket on the refrigerant which hinders or retards evaporation of the liquid refrigerant contained in the evaporator.

The object of the present invention is to provide means whereby the accumulation of oil is prevented in a certain part of an evaporator of a refrigerating system so that the accumulation of oil in the remainder of the evaporator will not hinder or retard normal evaporation of refrigerant contained therein.

Another object of the present invention is to provide an evaporator of a refrigerating system with means whereby refrigerant vaporizing in a body of liquid refrigerant, contained in the evaporator, and having a layer of oil floating thereon will not be required to flow through the layer of oil upon evaporating from the body of liquid refrigerant in the evaporator. In carrying out myinvention I utilize the velocity of refrigerant entering an evaporator and also the energy expended by the partial vaporization or flashing of the incoming refrigerant for intermittently flushing or removing lubricant, if anyis present, from a conduit or passage through which refrigerant vaporizing in the body of liquid refrigerant may flow to the space above the liquid level in the evaporator without passing through the main layer of lubricant accumulated in the evaporator.

Another object of the invention s to utilize the liquid refrigerant and the boiling effect of the liquid refrigerant to dissolve orpartially dissolve the layer of oil so as to decrease the blanketing effect of such oil.

Further objects and advantages of the 1931. Serial No. 533,995.

present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a pre ferred form of the present invention is clearly shown.

In the drawing:

Fig. 1 is a vertical section through a portion of an evaporator having my invention embodied therein and having refrigerant liq uefying unit shown diagrammatically con nected with the evaporator; and

Fig. 2 is a sectional view of a portion of tithe evaporator taken on the lines 22 of For the purpose of illustrating the presentinvention I have shown in Fig. 1 a compressor-condenser-expander type of refrigerating system having evaporator shown in section on a large scale and including connections 11 and 12 for operatively connecting the evaporator with the system. In addition to the evaporator, the system includes a compressor 1.3, a condenser 14, and a reservoir or liquid refrigerant tank 15. Refrigerant vapor is withdrawn from the evaporator 10 through the vapor or low pressure conduit 16 and is liquefied in the condenser 14 and returned to the evaporator through the liquid or high pressure conduit 17. The compressor is operated by a motor 18 controlled by an automatic switch 19 which may be actuated in response to the refrigerating demand, for example, by a pressure responsive device 21 connected to the low pressure conduit 16. It is obvious, insystems of the type disclosed, that the pressure responsive device 21, which actuates the switch 19 for controlling the electric circuit to the motor, is adjusted to operate between certain pressure limits. Since pressures and temperatures of the refrigerant increase or decrease uniformly it is apparent that the device 21 is adapted to maintain cer tain predetermined temperature limits Within the evaporator of the system.

At the beginning of operation of the syste the period of time between starting of the motor and the compressor and stopping thereof is referred to as the on phase of a cycle of operation of the refrigerant liquefying unit. The period of time between two successive operating periods or on phases of the refrigerant liquefying unit is referred to as an off phase of a cycle of operation of the unit. Thus, it is apparent that while the system is in operation to produce refrigeration, the refrigerant liquefying unit is cyclically operated and that each cycle therein includes an on phase and an off phase.

Referring to Fig. 1, evaporator comprises a header 24 forming a reservoir for liquid refrigerant, and a plurality of ducts 25 depending from the header 24 for circulating refrigerant to a point remote from the reservoir.v The li uid refrigerant indicated at 26 is prevented rom rising above a certain level 27 by a valve 28 which controls a liquid refrigerant opening 29 extending from the connection 11 through an end plate 30. Valve 28 is actuated in response to the liquid refrigerant level by the float 31. Float 31 is pivotally mounted as at 32 to a member 33, which member is secured in any suitable manner to an inwardly extending boss 34 formed on the plate 30. Liquid refrigerant is supplied to the evaporator through the inlet connection 11 and the vapor or gaseous refrigerant is withdrawn through the connection 12 connected to the vapor conduit 16.

The compressor of such system is lubricated by placing a quantity of oil in the crankcase thereof in which the oil is splashed by the rotating parts to distribute the o l throughout the compressor. Some of the 011 is dissolved in the refrigerant and some of the oil is mechanically pumped by the compressor to the condenser and reservoir and eventually to the evaporator. The 011 111 581)- arating'by gravity from the liquid refrigerant in the evaporator and rises to the top surface thereof due to its specific welght being less than that of the liquid refrigerant.

Refrigerant also evaporates from the body of liquid in the evaporator leaving the 011, whlch collects in a layer of from one-half inch to one and one-quarter inch thick on top of the refrigerant. This layer of oil on top of the refrigerant in the evaporator becomes more viscous as the temperature of the evaporator is reduced and forms a heavy blanket on top of the liquid refrigerant and impairs vaporization of the refrigerant and impairs the flow of refrigerant to the space above the layer of lubricant.

This collection or accumulation of oil in the evaporator is particularly harmful when the system is used to refrigerate an ice cream cabinet or the like, wherein very low temperatures are desired to be maintained. Under such conditions within the evaporator of the system, the compressor will be operated frequently and only for short intervals of time, thus causing short operating cycles of the compressor. These short cycles of the compressor are caused by the compressor creating a suction in the low pressure conduit 16 and in the space above the liquid level within the header 24 of the evaporator, sufficient to cause the pressure responsive device 21 to actuate the automatic switch 19 andbreak the electric circuit to the motor 18,

thus stoppin the compressor, without breaking up the ayer of oil in the evaporator, thereby preventing evaporation of liquid re frigerant from the body thereof below the layer of oil. Obviously, such short cycles of the compressor will continue for a while and the evaporator will not be reduced to the temperature at which the pressure responsive device 21 has been set to maintain therein. Consequently, the motor which drives the compressor is stopped before the refrigerant vaporizes and therefore the desired temperature will not be maintained. During these short cycles the refrigerant temperature rises and consequently the pressure increases below the oil. When this pressure During short operating cycles of the com- P pressor, as hereinbefore described, it is obvious that the layer or blanket of lubricant floating on the liquid refrigerant within the evaporator will cause a pressure differential in the evaporator. This pressure differential is caused by the Weight of the lubricant together with its viscosity and its adhesion to walls of the evaporator. This inherent characteristic is commonly referred to as the static head of the lubricant. Such pressure. differential permits the space in the evaporator above the layer of oil to be reduced, by suction of the compressor, considerably more than the static pressure of the liquid refrigerant below the oil. Under normal conditions, with a minimum amount or thickness of a layer 'of oil in the evaporator, this pressure differential is not as great as under normal condit ons when a large quantity or thick layer of oil is contained in the evaporator. However, under all conditions, when the compressor operates, there is a sufficient pressure dlfferential to cause the pressure responsive device to actuate and stop operation of the compressor before the pressure is substantially equalized throughout the entire interior of the evaporator. Thus the layer of oil creates a lag of considerable extent in evaporation of the refrigerant unless a by-pass, for the vaporized refrigerant in the body of liquid refrigerant, is provided through or around the oil layer so that it is not necessary for vaporized refrigerant to overcome the blanketing effect of the oil.

My invention is directed to a system where- I by vaporized refrigerant beneath a layer of oil in an evaporator by-passes the oil or is permitted to evaporate into the space above 1 the oil. This thereby permits liquid refrigermay extend around or through the layer of oil on the liquid refrigerant and which is in open communication with the body of liquid refrigerant and with the space above the oil floating on the liquid refrigerant in the evaporator. It is obvious that oil separating from the liquid refrigerant in an evaporator em ploying such a by-pass or confined passage will in a short time accumulate and form a layer or blanket in the passage of equal thickness to the oil layer floating on the liquid refrigerant in the main body thereof in the evaporator.

Such accumulation of oil in a by-pass of the type described particularly occurs in evaporators employed to produce and maintain a very low constant temperature. Under such conditions refrigerant within the bypass and below the oil therein ordinarily does not absorb enough heat to create sufficient vaporized refrigerant and consequently pressure in such a by-pass to cause the oil to be discharged from the by-pass. The bypass conduit or confined passage therefore becomes ineflicient for the purpose it was intended and will not produce the desired results. In view of this difficulty some means must be provided in an evaporator employing a by-pass of the type described whereby oil collecting in the by-pass will be intermittently removed or flushed from the by-pass conduit so as to afford a confined passage from the body of liquid refrigerant in the evaporator to the space above the oil floating thereon which is substantially devoid of oil. This is essential so that refrigerant vaporizing from the body of liquid thereof can freely flow therefrom Without being impeded by the viscous layer of oil. Since the interior of the evaporator is maintained at a considerably lower pressure than the pressure existing in the h gh pressure portion of the system, which includes the conduit 17, liquid refrigerant will flow into the evaporator very rapidly when the valve 28 opens. This liquid refrigerant upon enter ng the evaporator will immediately be reduced in pressure and some of the liquid refrigerant evaporates or flashes into vapor. I therefore utilize the velocity of the liquid refrigerant as it enters the evaporator and also the energy expended by the partial evaporation thereof to intermittently remove oil which may have separated and accumulated in the by-pass conduit or confined passage from the passage.

By intermittently removing oil, in the manner explained, from a by-pass of the type described, I provide a passage for refrigerant vaporizing from the body of liquid thereof, to the space above the oil floating on the liquid refrigerant in which passage the collection of oil is substantially eliminated. By providing a bypass conduit or confined passage in the evaporator, in which passage oil is substantially prevented from accumulating, the body of liquid refrigerant-below oil floating thereon is not subjected to the static head or blanketing effect thereof. Consequently, pressures and temperatures throughout the entire interior of an evaporator are substantially equalized and refrigerant below the oil can evaporate under normal corditions. Therefore short operating cycles of the compressor and splashing of liquid refrigerant into the gaseous refrigerant outlet of the evaporatorwill be eliminated. Thus the. pressure responsive device which actu ates the electric switch to start and stop the motor connected with the compressor is rendered more eflicient for controlling cyclical operations of the system between certain predetermined definite pressures and the evaporator thereof maintains a constant and uniform temperature.

Referring now to Fig. 1 I have pro-' vided means to eliminate the difficulties of a refrigerating system as hereinbe- .fore pointed out. This means includes a by-pass conduit or confined passage 40 formed in the member 33 and extending through or around the layer of oil 41 so as to be in open communication with the body of liquid refrigerant 26 and with the space in the evaporator above the oil layer 41. The by-pass conduit 40 is connected with and receives liquid refrigerantfrom the inlet opening 29 and is sealed therefrom by the valve 28. Bypass conduit 40 extends a. considerable distance upwardly from the top surface of the layer of oil 41 so as to discharge liquid re- During operation of the system, as previously described, the compressor upon being operated Withdraws gaseous refrigerant from the evaporator 10 and reduces the pressure therein, thus causing more refrigerant to evaporate from the body of liquid thereof.

As liquid refrigerant evaporates it is obvious I. .1

- to the cylical operation of the system. This action causes liquid refrigerant under high pressure upon entering the evaporator, which is maintained at a considerable lower pressure, to partially evaporate or flash into vapor as it flows into the evaporator. This incoming liquid refrigerant will flow very rapidly into the evaporator. When the compressorst-arts, to cause liquid refrigerant to enter the evaporator, as explained, this liquid will flow upwardly through the by-pass conduit or confined passage 40, communicating with the inlet opening 29, due to the difference in pressure below and above the liquid level in the evaporator caused by suction of the compressor, and also due to the partial evaporation of the incoming liquid refrigerant. The velocity of the upward flow of the liquid refrigerant as it enters the evaporator through the passage 40, together with the partial vaporization thereof, causes any oil, which might have separated from liquid refrigerant beneath the passage during the idle orfoff phase of. the compressorand, accumulated in the confined passage 40fto be removed or flushed therefrom. Continued discharge of liquid refrigerant, during operation of the compressor, through the inlet opening, which it is to be understood includes the confined passage 40, to a point above the layer of oil 41, causes the oil blanket ontop of the main body of liquid'refrigerant in the evaporator to be agitated or broken up. Discharging of liquid refrigerant which is substantially free of oil, as it enters the evaporator, on .the top surface of the separated oil 41, which oil is substantially free of liquid refrigerant except for the small quantity which is miscible therewith dissolves or partially dissolves some of the oil and in addition creates a disturbance of the oil blanket. This disturbance is due to the evaporation of some of the refrigerant'on the oil and also to the tendency 'of the substantially pure liquid refrigerant to mix with the dil or to settle or gravitate through the oil into the body of liquid refrigerant' therebelow, which refrigerant is saturated with as mnch oil as it is capable of holding. This disturbance tends to form a'region? of scum on the oil, thereby thinning the layer and disturbing its blanketing effect or static head at this point within the evaporator. By agitating or disturbing the blanketing effect of the layer of oil on the mam body of liquid refrigerant within the evaporator, refrigerant vaporizing from the body of liquid refrigerant will then be permitted to more freely flow through the oil and into the gaseous refrigerant space above the oil.

After the compressor stops and the entrance of liquid refrigerant to the evaporator is minimized, liquid within the evaporator then becomes substantially dormant and the oil will again form a thicker blanket. However, my improved device overcomes the difliculties heretofore encountered in evaporators during this dormant period or off phase of the compressor. Normal evaporation of refrigerant within the evaporator may continue in my improved apparatus during this relative dormant period due to the provision of the by-pass conduit substantially free of the accumulation of oil therein, and provides a passage through or around the blanket of oil for refrigerant vaporizing in the body of liquid refrigerant to the space above the oil. It is apparent that since the by-pass conduit 40 extends into the lower portion of the body of liquid refrigerant in the evaporator and since the liquid refrigerant in this portion contains only the small amount of oil in solution therewith, that separation of oil by gravitation from'this portion of the liquid refrigerant will be practically nil and therefore very little oil will accumulate in the confined passage 40. Since the collection of oil will be very little in the passage 40, during the relative dormant period within the evaporator, its blanketing effect will not be sufficient to retard normal evaporation of the vaporized refrigerant from the body of liquid thereof and this vaporization or evaporation will be of sufficient force to remove the small quantity of oil from the confined passage.

From the foregoing, it is apparent that I have provided an improved apparatus which is sure in its operation and which functions efiiciently when the system is operating to maintain a very low temperature while at the same time providing means for preventing the lubrication from retarding evaporation of liquid refrigerant in the evaporator. \Vith the hereinbefore enumerated difiiculties eliminated, evaporators employed to produce very low temperatures are rendered more efiicient for maintaining a constant range of temperature. Likewise the life of the compressor and its operating motor is prolongedbythe prevention of the heretofore described short operating cycles thereof.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow. What is claimed is as follows:

or confined passage, which is maintained 1. In a refrigerating system of the type in which a body of liquid refrigerant is maintained in an evaporator and in which a layer of lubricant floats on the liquid refrigerant in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, conduit means in open communica tion with the body of liquid refrigerant withing said evaporator and with the space above the layer of lubricant floating on the liquid refrigerant, said conduit means being arranged to receive liquid refrigerant as it enters said evaporator through the inlet opening thereof.

2. In a refrigerating system of the type in which a body of liquid refrigerant is maintained in an evaporator and in which a layer of lubricant floats on the liquid refrigerant in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, said inlet opening including a confined passage communicating with the body of liquid refrigerant within said evaporator and with the space above the lubricant floating on the liquid refrigerant.

3. In a refrigerating system of the type in which a body of liquid refrigerant is maintained in an evaporator and in which a layer of lubricant floats on the liquid refrigerant in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, means for preventing liquid refrigerant in'said evaporator from rising above a predetermined level including a valve, a confined passage within the evaporator for refrigerant evaporating, from the body of liquid refrigerant in said evaporator, into the space above the layer of lubricant floating on the liquid refrigerant, said passage communicating with the liquid refrigerant inlet opening of said evaporator, said valve controlling the flow of liquid refrigerant to said evaporator through said confined passage.

4. In a refrigerating system of the type in which a body of liquid refrigerant is maintained in an evaporator and in which a layer of lubricant floats on the liquid refrigerant in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level including a valve for controlling the inlet opening of said evaporator, said liquid refrigerant inlet opening including a confined passage communieating with the body of liquid refrigerant in said evaporator and with the space above the lubricant floating on the liquid refrigerant.

in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level, means for supplying liquid refrigerant to and for withdrawing gaseous refrigerant from said evaporator, means for starting and stopping said second named means, conduit means in open com munication with the body of liquid refrigerant within said evaporator and with the space above the layer of lubricant floating on the liquid refrigerant, said conduit means being arranged to receive liquid as it enters the evaporator through said inlet opening during the operating phase of a cycle of said second named means due to the cyclical operation of the system.

6. In a refrigerating system of the type in which a body of liquid refrigerant is maintained in an evaporator and in which a layer of lubricant floats on the liquid refrigerant in the evaporator, the combination of an evaporator having a liquid refrigerant inlet opening, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level, means for supplying liquid refrigerant to and for withdrawing gaseous refrigerant from said evaporator, means for starting and stopping said second named means, said liquid refrigerant inlet opening communicating with the body of liquid refrigerant within said evaporator and with the space above the layer of lubricant floating on the liquid refrigerant, said inlet opening being controlled by said first named means and arranged to receive liquid refrigerant as it enters the evaporator during the operating phase of a cycle of said second named means due to the cyclical operation of the system.

7. In a refrigerating system employing a refrigerant and a lubricant as a working fluid, the combination of an evaporator having a liquid refrigerant inlet opening, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level, a lubricant accompanying the liquid refrigerant delivered to said evaporator and separable by gravitation within. the evaporator from liquid refrigerant contained therein, a confined passage connected with said inlet opening of said evaporator, said passage communicating with the space above the lubricant separated from the refrigerant in said evaporator and with the body of liquid refrigerant beneath the separated lubricant, said means controlling the flow of incoming liquid refrigerant to said evaporator through said inlet opening and said passage.

8. In a refrigerating apparatus, the combination of an evaporator to which liquid refrigerant heavier than oil and mixed there'- with is supplied, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level, and a by-pass for conducting vaporized refrigerant, from the body of liquid refrigerant in said evaporator, through the oil thereon, said by-pass being in communication with a portion of said means whereby liquid refrigerant being supplied to said evaporator is caused to flow through said by-pass before entering the main body of liquid within the evaporator.

9. In a refrigerating apparatus, the combination of an evaporator including a receptacle and duct means extending therefrom and in communication therewith, a liquid refrigerant heavier than oil and mixed therewith supplied to said evaporator, means for preventing liquid refrigerant in said evaporator from rising above a predetermined level, and a by-pass for conducting vaporized refrigerant, from said duct means and from the body of liquid refrigerant in said receptaele, through the oil on the liquid refrigerant, said by-pass being in communication with a portion. of said means whereby liquid refrigerant being supplied to said evaporator is caused to flow through said by-pass before entering the main body of liquid within the evaporator.

In testimony whereof I hereto affix my signature.

WARREN H. F. SCHMIEDING. 

